Teachers Note:

Description: Visualise the influence of both the Moon and the Sun on the ocean’s tides. Plan holidays in Biarritz for one surfer, one scuba diver and one sports fisher depending on the tide coefficients of this period.

Objective(s): Understand the phenomenon of the ocean tide and its influence on the activities related to the sea. Learn how to use a tide coefficient table.

Hints:

• The Moon is 385 000 kilometres from the Earth. From that distance the Earth attracts the Moon by its force of gravity, but the Moon also exerts a force of gravity on our planet! The Moon has an elliptical orbit, not a circular one. When the moon is closest to the Earth (perigee), the tide-producing force is 20% greater than the average, and when it is furthest away (apogee), the force is 20% less than the average. The time between successive perigees is 27.5 days. But the Moon is relatively small and only exerts a visible influence on the distortable surfaces of the Earth, i.e. the oceans’ waters. The water levels of the surfaces closest to the Moon rise by about ten meters. A few hours later, when the Moon has turned away, water levels normalise. From time to time, the Sun “helps” the Moon and tides reach maximum intensity. The answer to the first activity is that the tide is stronger in case 1, because the Sun’s and the Moon’s forces are added. .
• Using the table, taking the example of 1st July:
  • The low tide beginning at 1:07 in the morning, getting high at 6:44 and finishing at 13:38 (low again) has a coefficient of 80, which allows Nicole to scuba dive and Iñaki to go fishing, even if this is a limited coefficient. For Eric, this coefficient of 80 corresponds to medium-sized waves.
  • The tide beginning at 13:38 in the afternoon (low) getting high at 19:13 and finishing at 02:09 on the next morning (low again) has a coefficient of 85, which does not allow Nicole to scuba dive and Iñaki to go fishing. Eric can get bigger waves than in the morning.

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